The present invention relates to a braiding yarn made of expanded graphite for a gland packing which is to be used in a shaft seal part of a fluid apparatus or the like, and more particularly to a braiding yarn made of expanded graphite which can enhance the pressure resistance of a gland packing.
Conventionally, as a braiding yarn for a gland packing which is to be used in a shaft seal part of a fluid apparatus or the like, known is, for example, a braiding yarn 1 shown in FIG. 8. In the braiding yarn 1, an expanded graphite tape 2 of a predetermined width is folded into a valley fold in the longitudinal direction, and the outer periphery of the tape is covered by a reinforcing member 3 configured by a braided body of a metal wire.
A gland packing is produced by bundling and braiding a plurality of the braiding yarns 1. However, the expanded graphite tape 2 is low in tensile strength and brittle, and edges of both end portions 2a, 2b in the width direction have low flaking resistance among expanded graphite particles. In edges of both end portions 2a, 2b in the width direction, namely, expanded graphite particles easily flake off. In the case where, during a braiding process, large tensile and sharing forces act on the edges of both end portions 2a, 2b in the width direction, therefore, cracks are formed with starting from the edges of both the end portions 2a, 2b in the width direction, and expanded graphite particles in and in the vicinity of the edges of both the end portions 2a, 2b in the width direction flake off. When a plurality of braiding yarns are to be braided, consequently, a large tensile force cannot be applied to the braiding yarns, so that the tensile force of the braiding yarns is limited to a low level. As a result, the pressure resistance of a gland packing cannot be enhanced.
It is an object of the invention to provide a braiding yarn made of expanded graphite in which flaking of expanded graphite particles during a braiding process is reduced or prevented from occurring, and the pressure resistance of a gland packing can be enhanced.
In order to attain the object, the braiding yarn made of expanded graphite according to the invention is characterized in that, in a braiding yarn made of expanded graphite which is to be used in a gland packing, an outer periphery of a bent expanded graphite tape is covered by a reinforcing member configured by a knitted body or a braided body, and at least one end portion in a width direction of the expanded graphite tape is bent to be directed toward an inner side in the width direction of the braiding yarn.
Furthermore, the braiding yarn made of expanded graphite according to the invention is characterized in that, in a braiding yarn made of expanded graphite which is to be used in a gland packing, an outer periphery of a twisted expanded graphite tape is covered by a reinforcing member configured by a knitted body or a braided body, and at least one end portion in a width direction of the expanded graphite tape is bent to be directed toward an inner side in the width direction of the braiding yarn.
According to the inventions, it is a matter of course that cutting of the bent or twisted expanded graphite tape which may be caused by a tensile or twisting force during a braiding process is effectively prevented from occurring by the reinforcing member covering the outer periphery of the tape. Since at least one end portion in the width direction of the expanded graphite tape is bent to be directed toward the inner side in the width direction, moreover, large tensile and sharing forces do not directly act on the edges of the one end portion during a braiding process, and hence occurrence of cracks from the edges of the one end portion and flaking of expanded graphite particles due to the occurrence of cracks can be reduced. As a result, braiding at a larger tensile force is enabled, and the pressure resistance of a gland packing can be enhanced.
Furthermore, the braiding yarn made of expanded graphite according to the invention is characterized in that reinforcing fibers are embedded in the expanded graphite tape. According to the invention, since reinforcing fibers are embedded in the expanded graphite tape, the tensile and twisting forces of the expanded graphite tape can be improved.
Furthermore, the braiding yarn made of expanded graphite according to the invention is characterized in that part of expanded graphite particles on a side of a surface of the expanded graphite tape are removed away. According to the invention, part of expanded graphite particles which are on the side of the surface of the expanded graphite tape, and which are highly oriented at a high density where cracks easily occur are removed away by a blasting process. During a braiding process, even when a large tensile force acts on the expanded graphite tape, therefore, occurrence of cracks and flaking of expanded graphite particles due to the occurrence of cracks can be reduced more surely.